One of the fears some members of the public have about vaccines is the erroneous idea that there are too many vaccines being given and that it would overwhelm a person's immune system. Understandable why they think that & reflects inadequate understanding of how vaccines work.
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100 years ago we just had one vaccine vs Smallpox.
70 years ago we had 5 vs diphtheria, tetanus, pertussis, polio & smallpox.
Now, more than a dozen are given by the age of 1.
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Some are concerned vaccines might weaken the immune system. However, even infants have the capacity to respond to an enormous number of antigens (that's the proteins that our immune system generates a response to). Theoretical capacity 10 billion to 1000 billion antigens!
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For perspective , we are exposed to thousands to millions of antigens every day normally!

Children are exposed to fewer antigens in vaccines today than in the past. Advances in protein chemistry & vaccine science have resulted in vaccines containing fewer antigens.
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So the relevance for today - the COVID mRNA vaccines will be highly purified. Means lower risk of unwanted side effects. And the body's immune system will be trained to respond to the virus antigen (spike protein) which is what we want and need.